Mounting structure

ABSTRACT

A mounting structure includes an electronic component mounted on a circuit board. Land electrodes are disposed on a board body and are connected to outer electrodes of the electronic component through solders, respectively. A distance from each of the land electrodes to a top of the corresponding solder is not larger than about 1.27 times a distance from each of the land electrodes to an exposed portion of a capacitor conductor exposed at an end surface of the electronic component, the capacitor conductor being positioned closest to the circuit board.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mounting structure, and moreparticularly to a mounting structure in which an electronic component,such as a capacitor, is mounted on a board.

2. Description of the Related Art

In an electronic component made up of dielectric layers and capacitorconductors successively laminated (stacked) on each other, when an ACvoltage is applied to the electronic component, the applied voltagecauses distortions induced by an electric field in the dielectriclayers. Those electric-field induced distortions vibrate a board onwhich the electronic component is mounted, thereby generating vibrationsounds called “acoustic noise”. As an invention concerning a related-artelectronic component intended to reduce the “acoustic noise”, there isknown, for example, Japanese Unexamined Patent Application PublicationNo. 2000-232030 that discloses a circuit board mounting method for amonolithic ceramic capacitor.

According to the circuit board mounting method for the monolithicceramic capacitor, which is disclosed in Japanese Unexamined PatentApplication Publication No. 2000-232030, two capacitors having the samespecifications are arranged on a front surface and a rear surface of acircuit board. With that arrangement, vibration transmitted (propagated)from one capacitor to the circuit board and vibration transmitted fromthe other capacitor to the circuit board cancel each other. As a result,the “acoustic noise” is reduced.

However, the circuit board mounting method for the monolithic ceramiccapacitor, disclosed in Japanese Unexamined Patent ApplicationPublication No. 2000-232030, has the problem that the degree of freedomin circuit design is reduced because of the necessity of mounting twocapacitors on both the surfaces of the circuit board.

SUMMARY OF THE INVENTION

Accordingly, preferred embodiments of the present invention provide amounting structure which significantly reduces acoustic noise whilemaintaining a high degree of freedom in circuit design.

According to a first preferred embodiment of the present invention, amounting structure includes an electronic component mounted on a board,wherein the electronic component includes a substantially rectangularparallelepiped laminate including a plurality of laminated dielectriclayers, and including a mounting surface that faces the board and thatis positioned on one side of the laminate in a lamination direction, anda first end surface and a second end surface that are opposed to eachother, a plurality of capacitor conductors laminated together with thedielectric layers to define a capacitor, and led out to the first endsurface or the second end surface, a first outer electrode disposed toextend over the first end surface and partly over the mounting surface,and connected to the capacitor conductors, a second outer electrodedisposed to extend over the second end surface and partly over themounting surface, and connected to the capacitor conductors, wherein theboard includes a board body, and a first land electrode and a secondland electrode disposed on the board body, the first land electrode andthe second land electrode being connected respectively to the firstouter electrode and the second outer electrode through conductivematerials, and wherein a distance from the first land electrode or thesecond land electrode to a top of the conductive material is not largerthan about 1.27 times a shortest one among distances from the first landelectrode or the second land electrode to exposed portions of thecapacitor conductors, which portions are exposed at the first endsurface or the second end surface.

According to a second preferred embodiment of the present invention, amounting structure includes an electronic component mounted on a board,wherein the electronic component includes a substantially rectangularparallelepiped laminate including a plurality of laminated dielectriclayers, and including a mounting surface that is faces the board andthat is positioned on one side of the laminate in a directionperpendicular or substantially perpendicular to a lamination direction,and a first end surface and a second end surface that are opposed toeach other, a plurality of capacitor conductors laminated together withthe dielectric layers to define a capacitor, and led out to the firstend surface or the second end surface, a first outer electrode disposedto extend over the first end surface and partly over the mountingsurface, and connected to the capacitor conductors, a second outerelectrode disposed to extend over the second end surface and partly overthe mounting surface, and connected to the capacitor conductors, whereinthe board includes a board body, and a first land electrode and a secondland electrode disposed on the board body, the first land electrode andthe second land electrode being connected respectively to the firstouter electrode and the second outer electrode through conductivematerials, and wherein the first land electrode is divided into a firstland portion and a second land portion, the first land portion and thesecond land portion are not overlapped with a central portion of thefirst end surface when looking at the laminate in a plan view from adirection normal to the board body, and the conductive material is notoverlapped with the central portion of the first end surface whenlooking at the laminate in a plan view from the direction normal to theboard body.

In the mounting structure according to the first preferred embodiment,since the distance from the first land electrode or the second landelectrode to the top of the conductive material is not larger than about1.27 times the shortest one among the distances from the first landelectrode or the second land electrode to exposed portions of thecapacitor conductors, which portions are exposed at the first endsurface or the second end surface, the conductive materials acting astransmission media for vibration, which is generated in a portion of thelaminate including the capacitor conductors, is positioned apart from aportion of the laminate, which portion vibrates in a maximum magnitude.As a result, the vibration is less transmittable to the circuit board.

In the mounting structure according to the second preferred embodiment,since the first land portion and the second land portion are notoverlapped with the central portion of the first end surface whenlooking at the laminate in a plan view from the direction normal to theboard body and the conductive material is also not overlapped with thecentral portion of the first end surface when looking at the laminate ina plan view from the direction normal to the board body, the landelectrode and the conductive material acting as transmission media forvibration, which is generated in a portion of the laminate including thecapacitor conductors, are not connected to a portion of the laminate,which portion vibrates in a maximum magnitude. As a result, thevibration is less transmittable to the circuit board.

With various preferred embodiments of the present invention, sincevibration is dampened even when only one electronic component ismounted, the acoustic noise can be reduced while a high degree offreedom can be obtained in circuit design.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional structural view of a mounting structure accordingto a first preferred embodiment of the present invention.

FIG. 2 is a plan view of the mounting structure according to the firstpreferred embodiment of the present invention.

FIG. 3 is an external perspective view of an electronic componentaccording to the first preferred embodiment of the present invention.

FIG. 4 is an exploded perspective view of a laminate of the electroniccomponent illustrated in FIG. 3.

FIG. 5 illustrates a state where the electronic component vibrates inthe first preferred embodiment of the present invention.

FIG. 6 is a schematic view of a device for measuring a sound pressurelevel.

FIG. 7 is a graph representing experimental results with the firstpreferred embodiment of the present invention.

FIG. 8 is a sectional structural view of a mounting structure accordingto a first modification of a preferred embodiment of the presentinvention.

FIGS. 9A and 9B are each a sectional structural view of an electroniccomponent constituting a mounting structure according to a secondmodification of a preferred embodiment of the present invention.

FIG. 10 is a plan view of a mounting structure according to a thirdmodification of a preferred embodiment of the present invention.

FIG. 11 is a graph representing experimental results with the thirdmodification of a preferred embodiment of the present invention.

FIG. 12 is a sectional structural view of a mounting structure accordingto a second preferred embodiment of the present invention.

FIG. 13 is a plan view of the mounting structure according to the secondpreferred embodiment of the present invention when viewed from thepositive side in a z-axis direction.

FIG. 14 illustrates a state where the electronic component vibrates inthe second preferred embodiment of the present invention.

FIG. 15 is a graph representing experimental results with the secondpreferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A mounting structure according to various preferred embodiments of thepresent invention will be described below with reference to theaccompanying drawings. It is to be noted that similar members andcomponents are denoted by common reference symbols in the drawings andduplicate description is omitted.

First Preferred Embodiment

First, a mounting structure 1 according to a first preferred embodimentis described with reference to FIGS. 1 to 4. As illustrated in FIGS. 1and 2, the mounting structure 1 includes an electronic component 10 anda circuit board 50. The electronic component 10 preferably is a chipcapacitor, for example, and is mounted on the circuit board 50. As alsoillustrated in FIGS. 3 and 4, the electronic component 10 includes alaminate 11, outer electrodes 12 (12 a and 12 b), and capacitorconductors 30 (30 a to 30 d) and 32 (32 a to 32 d). In the followingdescription, a lamination direction in which multiple layers arelaminated in the laminate 11 is defined as a z-axis direction. Adirection in which a long side of the laminate 11 extends when lookingat the laminate 11 in a plan view from the z-axis direction is definedas an x-axis direction. A direction in which a short side of thelaminate 11 extends when looking at the laminate 11 in a plan view fromthe z-axis direction is defined as a y-axis direction.

As illustrated in FIG. 3, the laminate 11 preferably has a substantiallyrectangular parallelepiped shape including a top surface S1 and a bottomsurface S2 positioned at both ends of the laminate 11 in the z-axisdirection, end surfaces S3 and S4 opposed to each other, and lateralsurfaces S5 and S6 opposed to each other. The laminate 11 is preferablychamfered such that corners and ridges of the laminate 11 are rounded,for example. In the following description, a surface of the laminate 11,which is positioned on the positive side in the z-axis direction, isdefined as the top surface S1, and a surface of the laminate 11, whichis positioned on the negative side in the z-axis direction, is definedas the bottom surface S2. Further, a surface of the laminate 11, whichis positioned on the negative side in the x-axis direction, is definedas the end surface S3, and a surface of the laminate 11, which ispositioned on the positive side in the x-axis direction, is defined asthe end surface S4. A surface of the laminate 11, which is positioned onthe positive side in the y-axis direction, is defined as lateral surfaceS5, and a surface of the laminate 11, which is positioned on thenegative side in the y-axis direction, is defined as the lateral surfaceS6. The bottom surface S2 serves as a mounting surface that ispositioned to face the circuit board 50 when the electronic component 10is mounted to the circuit board 50.

The laminate 11 is preferably constructed, as illustrated in FIG. 4, bylaminating a plurality of ceramic layers (dielectric layers) 17 (17 a to17 n) such that the ceramic layers 17 are successively stacked in theorder from the positive side to the negative side in the z-axisdirection. Each ceramic layer 17 preferably is substantially rectangularand is made of a dielectric ceramic, for example. In the followingdescription, a principal surface of the ceramic layer 17 on the positiveside in the z-axis direction is called a front surface, and a principalsurface of the ceramic layer 17 on the negative side in the z-axisdirection is called a rear surface.

The top surface S1 of the laminate 11 is constituted by a front surfaceof the ceramic layer 17 a that is disposed on the most positive side inthe z-axis direction. The bottom surface S2 of the laminate 11 isconstituted by a rear surface of the ceramic layer 17 n that is disposedon the most negative side in the z-axis direction. Further, the endsurface S3 is constituted by continuously laminated short sides of theceramic layers 17 a to 17 n on the negative side in the x-axisdirection. The end surface S4 is constituted by continuously laminatedshort sides of the ceramic layers 17 a to 17 n on the positive side inthe x-axis direction. The lateral surface S5 is constituted bycontinuously laminated long sides of the ceramic layers 17 a to 17 n onthe positive side in the y-axis direction. The lateral surface S6 isconstituted by continuously laminated long sides of the ceramic layers17 a to 17 n on the negative side in the y-axis direction.

The capacitor conductors 30 a to 30 d and 32 a to 32 d are laminatedtogether with the ceramic layers 17 such that adjacent two of thecapacitor conductors are opposed to each other with the ceramic layer 17interposed therebetween.

As illustrated in FIG. 4, the capacitor conductors 30 a to 30 d aredisposed on surfaces of the ceramic layers 17 d, 17 f, 17 h and 17 j,respectively, and are incorporated in the laminate 11. The capacitorconductors 30 a to 30 d preferably are each substantially rectangularand are led out to the short sides of the ceramic layers 17 d, 17 f, 17h and 17 j on the positive side in the x-axis direction, respectively.With such an arrangement, the capacitor conductors 30 a to 30 d are ledout to the end surface S4 (first end surface), as illustrated in FIG. 1.

As illustrated in FIG. 4, the capacitor conductors 32 a to 32 d aredisposed on surfaces of the ceramic layers 17 e, 17 g, 17 i and 17 k,respectively, and are incorporated in the laminate 11. The capacitorconductors 32 a to 32 d preferably are each substantially rectangularand are led out to the short sides of the ceramic layers 17 e, 17 g, 17i and 17 k on the negative side in the x-axis direction, respectively.With such an arrangement, the capacitor conductors 32 a to 32 d are ledout to the end surface S3 (second end surface), as illustrated inFIG. 1. The capacitor conductors 30 a to 30 d and the capacitorconductors 32 a to 32 d are overlapped with each other when looking atthe laminate 11 in a plan view from the z-axis direction. As a result, acapacitor C is defined between the capacitor conductors 30 and 32.

The outer electrode 12 a (second outer electrode) covers the end surfaceS3, and it is folded to partly cover the top surface S1, the bottomsurface S2, and the lateral surfaces S5 and S6. In other words, theouter electrode 12 a is disposed to extend over not only the end surfaceS3, but also partly over the top surface S1, the bottom surface S2, andthe lateral surfaces S5 and S6. Furthermore, the outer electrode 12 a isconnected to the capacitor conductors 32 a to 32 d. More specifically,the outer electrode 12 a covers the entire end surface S3 of thelaminate 11 such that exposed portions of the capacitor conductors 32 ato 32 d exposed at the end surface S3 are covered with the outerelectrode 12 a.

The outer electrode 12 b (first outer electrode) covers the end surfaceS4, and it is folded to partly cover the top surface S1, the bottomsurface S2, and the lateral surfaces S5 and S6. In other words, theouter electrode 12 b is disposed to extend over not only the end surfaceS4, but also partly over the top surface S1, the bottom surface S2, andthe lateral surfaces S5 and S6. Furthermore, the outer electrode 12 b isconnected to the capacitor conductors 30 a to 30 d. More specifically,the outer electrode 12 b covers the entire end surface S4 of thelaminate 11 such that exposed portions of the capacitor conductors 30 ato 30 d, which are exposed at the end surface S4, are covered with theouter electrode 12 b.

The circuit board 50 is a multilayer board including circuits, notillustrated, on the surface and in the inside thereof. The circuit board50 includes a board body 52 and land electrodes 54 (54 a and 54 b). Theboard body 52 is preferably constituted by laminating a plurality ofinsulator layers, and includes a principal surface S11. As illustratedin FIG. 1, the principal surface S11 is a principal surface of the boardbody 52 on the positive side in the z-axis direction.

The land electrodes 54 are disposed on the principal surface S11 of theboard body 52 and are connected to the outer electrodes 12 a and 12 bthrough conductive materials (solders 60 a and 60 b). More specifically,as illustrated in FIG. 2, when looking at the laminate 11 in a plan viewfrom the z-axis direction, the land electrodes 54 a and 54 b preferablyare each substantially rectangular and are arranged in the order fromthe negative side to the positive side in the x-axis direction.

As illustrated in FIGS. 1 and 2, the outer electrodes 12 a and 12 b areplaced on the land electrodes 54 a and 54 b and are fixed to the landelectrodes 54 a and 54 b in states electrically connected theretothrough solders 60 a and 60 b, respectively. As illustrated in FIG. 1,the solders 60 a and 60 b not only fill respective gaps between theouter electrodes 12 a, 12 b and the land electrodes 54 a, 54 b, but alsoextend along respective portions of the outer electrodes 12 a and 12 b,which portions cover the lateral surfaces S3 and S4, toward the positiveside in the z-axis direction.

For the purpose of reducing the acoustic noise and increasing the degreeof freedom in circuit design, the mounting structure 1 is structured asfollows. First, heights or distances from surfaces (upper surfaces) ofthe land electrodes 54 a and 54 b on the positive side in the z-axisdirection to tops of the solders 60 a and 60 b are each defined as H1.The tops of the solders 60 a and 60 b imply ends of the solders 60 a and60 b, positioned on the positive side in the z-axis direction, whichextend over the outer electrodes 12 a and 12 b covering the lateralsurfaces S3 and S4, respectively. Further, the height implies a distancein the z-axis direction. In the following description, the height H1from each of the surfaces (upper surfaces) of the land electrodes 54 aand 54 b on the positive side in the z-axis direction to each of thetops of the solders 60 a and 60 b are also called a solder filletheight. Moreover, shortest ones among distances from the land electrodes54 a and 54 b to the exposed portions of the capacitor conductors 30 ato 30 d and 32 a to 32 d exposed at the end surfaces S3 and S4 are eachdefined by H2. In other words, H2 implies a height from each of the landelectrodes 54 a and 54 b to an exposed portion of the capacitorconductor 32 d exposed at the end surface S3, the capacitor conductor 32d being positioned closest to the circuit board 50. Given thosedefinitions, H1 is preferably set to be not larger than about 1.27 timesH2, for example.

A non-limiting example of a method of manufacturing the electroniccomponent 10 will be described below with reference to the drawings,specifically FIGS. 3 and 4.

First, ceramic slurry is obtained by adding a binder and an organicsolvent to ceramic powder of BaTiO₃, for example, putting them into aball mill, and wet-mixing those materials for preparation of the ceramicslurry. Then, a ceramic green sheet to be used as the ceramic layer 17is fabricated by coating the obtained ceramic slurry in the form of asheet over a carrier sheet with the doctor blade method, and drying thecoated ceramic slurry. A thickness of the ceramic green sheet to be usedas the ceramic layer 17 is preferably set such that the ceramic layerafter firing has a thickness of about 0.5 μm or more and about 10 μam orless, for example. It is noted that a main constituent of the ceramicpowder may be selected from CaTiO₃, SrTiO₃, CaZrO₃, etc. Furthermore, aMn compound, a Mg compound, a Si compound, a Co compound, a Ni compound,a rare-earth compound, etc. may be optionally added as an accessoryconstituent of the ceramic powder.

Next, the capacitor conductors 30 and 32 are each formed by coating apaste made of a conductive material over the ceramic green sheet to beused as the ceramic layer 17 with the screen printing method. The pastemade of the conductive material is prepared by adding an organic binderand an organic solvent to metal powder. The metal powder is optionallymade of, e.g., Ni, Cu, Ag, Pd, an Ag—Pd alloy, Au, etc. A thickness ofeach of the capacitor conductors 30 and 32 after firing is preferablyabout 0.3 μm or more and about 2.0 μm or less, for example.

Next, the ceramic green sheets to be used as the ceramic layers 17 arelaminated one above another, whereby a mother laminate before firing isobtained. The mother laminate before firing is then pressed.

Next, the mother laminate before firing is cut in a predetermined sizeto obtain a plurality of laminates 11 before firing. Surfaces of each ofthe laminates 11 before firing are then subjected to polishing, e.g.,barrel polishing.

Next, the laminate 11 before firing is fired. A firing temperature is,e.g., about 1200° C. to about 1300° C., for example.

Next, the outer electrodes 12 (12 a and 12 b) are formed on the laminate11 after the firing. More specifically, a conductive paste optionallycontaining Cu, Ni, Ag, Pd, an Ag—Pd alloy, Au, etc. is coated oversurfaces of the laminate 11 by suitable one of the known techniques,e.g., the dipping method or the slit method. An underlying electrode isthen formed by baking the conductive paste. Ni plating and Sn platingare carried out on the underlying electrode. As a result, the outerelectrodes 12 are formed. The electronic component 10 is completedthrough the above-described steps.

The electronic component 10 thus manufactured is mounted on the circuitboard 50. The board body 52 is constituted by laminating a plurality ofinsulator layers that are each made of, e.g., a glass epoxy resin.Further, the land electrodes 54 are each formed by coating a plated filmover an underlying electrode made of Cu. When mounting the electroniccomponent 10, a solder paste is first coated over the land electrode 54.The outer electrodes 12 of the electronic component 10 are then set onthe land electrodes 54, respectively, such that the bottom surface S2 ispositioned to face the principal surface S11 of the board body 52. Atthat time, the bottom surface S2 and the principal surface S11 arepreferably held parallel or substantially parallel to each other.Further, after carrying out a reflow process to melt the solder paste,the molten solder paste is solidified. As a result, the electroniccomponent 10 is mounted on the circuit board 50.

For example, a Sn—Pb eutectic solder or a lead-free solder, e.g., aSn—Ag—Cu alloy, can be used as the solder paste. Additionally, aconductive adhesive may be used instead of the solder 60.

With the mounting structure 1 thus constructed, it is possible to notonly reduce the acoustic noise, but also to provide a high degree offreedom in circuit design as described below. FIG. 5 illustrates a statewhere the electronic component 10 vibrates in the mounting structure 1.

As discussed above, the circuit board mounting method for the monolithicceramic capacitor, disclosed in Japanese Unexamined Patent ApplicationPublication No. 2000-232030, has the problem that the degree of freedomin circuit design is reduced because two capacitors are mounted to boththe surfaces of the circuit board in order to reduce the acoustic noise.

To cope with that problem, in the mounting structure 1, the height(solder fillet height) H1 from each of the surfaces of the landelectrodes 54 a and 54 b on the positive side in the z-axis direction toeach of the tops of the solders 60 a and 60 b is preferably set to benot larger than about 1.27 times the height H2 from each of the landelectrodes 54 a and 54 b to the exposed portion of the capacitorconductor 32 d exposed at the end surface S3, for example, the capacitorconductor 32 d being positioned closest to the circuit board 50. Underthose conditions, the mounting structure 1 can realize, as describedbelow, the reduction of the acoustic noise without using two electroniccomponents 10.

In more detail, in the mounting structure 1, vibration generated in aportion of the laminate 11 where the capacitor conductors 30 and 32 aredisposed is transmitted through the solders 60 and the land electrodes54, whereby the circuit board 50 is vibrated and the acoustic noise iscaused. As illustrated in FIG. 5, the electronic component 10 (i.e., thelaminate 11) vibrates in a larger magnitude at a position closer to acenter of each of the end surfaces S3 and S4 in the z-axis direction.Taking such a point into consideration, in the mounting structure 1, thesolders 60 each acting as a transmission path for the vibration aredisposed apart from the centers of the end surfaces S3 and S4 in thez-axis direction, which are vibration sources. With such an arrangement,the vibration generated in the electronic component 10 is lesstransmittable to the circuit board 50. As a result, the acoustic noiseis reduced in the mounting structure 1.

For more positively confirming the advantageous effects of the mountingstructure 1, the inventors of this application conducted experiments asfollows. In more detail, the inventors prepared a first sample group anda second sample group described below. In each of the first sample groupand the second sample group, the solder fillet height H1 was changed aslisted in the following condition.

Conditions for First Sample Group

Size of the circuit board: 100 mm×40 mm×1.6 mm

External dimensions of the electronic component: 1.75 mm×0.95 mm×0.91 mm

Capacitance of the electronic component: 22 μF

Thickness of the ceramic layer: 0.94 μm

Thickness of the capacitor conductor: 0.58 μm

Number of the capacitor conductors: 491

Height H0 (see FIG. 1) of the laminate: 0.87 mm

Solder fillet height: six different values, i.e., 0.08 mm, 0.16 mm, 0.32mm, 0.5 mm, 0.6 mm, and 0.8 mm

Gap H3 (see FIG. 1) between the outer electrode and the land electrode:0.05 mm

Thickness H4 (see FIG. 1) of the outer electrode: 20 μm

Distance H5 (see FIG. 1) from the capacitor conductor, which ispositioned closest to the circuit board, to the bottom surface of thelaminate (i.e., thickness of outer layer of the laminate): 56 μm

In the first sample group, the height H2 from the land electrode to theexposed portion of the capacitor conductor exposed at the end surface,the capacitor conductor being positioned closest to the circuit board,is a total (126 μm) of H3, H4 and H5.

Conditions for Second Sample Group

Size of the circuit board: 100 mm×40 mm×1.6 mm

External dimensions of the electronic component: 2.11 mm×1.35 mm×1.31 mm

Capacitance of the electronic component: 47 μF

Thickness of the ceramic layer: 0.94 μm

Thickness of the capacitor conductor: 0.62 μm

Number of the capacitor conductors: 671

Height H0 (see FIG. 1) of the laminate: 1.26 mm

Solder fillet height: five different values, i.e., 0.08 mm, 0.21 mm, 0.4mm, 0.75 mm, and 1.2 mm

Gap H3 (see FIG. 1) between the outer electrode and the land electrode:0.05 mm

Thickness H4 (see FIG. 1) of the outer electrode: 25 μm

Distance H5 (see FIG. 1) from the capacitor conductor, which ispositioned closest to the circuit board, to the bottom surface of thelaminate (i.e., thickness of outer layer of the laminate): 90 μm

In the second sample group, the height H2 from the land electrode to theexposed portion of the capacitor conductor exposed at the end surface,the capacitor conductor being positioned closest to the circuit board,is a total (165 μm) of H3, H4 and H5.

A suppression rate of a sound pressure level was measured on the firstsample group and the second sample group both prepared as describedabove. FIG. 6 is a schematic view of a device 71 for measuring a soundpressure level.

The inventors conducted the measurement by placing the mountingstructure 1 (i.e., each sample in the first sample group and the secondsample group) in an anechoic box 73, and by applying an AC voltage witha frequency of 3 kHz and a voltage of 1 Vpp to the electronic component10. Further, acoustic noise caused at that time was collected by a soundcollecting microphone 74, and a sound level of the collected acousticnoise was measured by using a sound collection meter 76 and an FETanalyzer 78 (CF-5220 made by Ono Sokki Co., Ltd.). The sound collectingmicrophone 74 was installed at a position away from the circuit board 50through a distance of 3 mm. FIG. 7 is a graph representing theexperimental results. In the graph, the vertical axis indicates thesuppression rate of the sound pressure level, and the horizontal axisindicates a value of H1/H2. The term “suppression rate of the soundpressure level” implies a rate at which the sound pressure level issuppressed in comparison with that in the case of H1/H2=8.

As seen from FIG. 7, in both the first sample group and the secondsample group, when H1/H2 is not larger than about 1.27, the suppressionrate of the sound pressure level is drastically increased in comparisonwith that when H1/H2 is larger than about 1.27. It is hence understoodfrom the experimental results that the acoustic noise can be reduced bysetting H1 to be not larger than about 1.27 times H2, for example.

First Modification of a Preferred Embodiment

A mounting structure 1 a according to a first modification of apreferred embodiment of the present invention will be described belowwith reference to the drawings. FIG. 8 is a sectional structural view ofthe mounting structure 1 a according to the first modification.

The mounting structure 1 a differs from the above-described mountingstructure 1 in positions of the capacitor conductors 30 and 32. Morespecifically, the capacitor conductors 30 and 32 of the mountingstructure 1 a are positioned on the more positive side in the z-axisdirection than the capacitor conductors 30 and 32 of the mountingstructure 1. In other words, a distance H5 between the bottom surface S2and the capacitor conductor 32 d is larger than a distance between thetop surface S1 and the capacitor conductor 30 a. With such anarrangement, the height H2 in the mounting structure 1 a from each ofthe land electrodes 54 a and 54 b to the exposed portion of thecapacitor conductor 32 d exposed at the end surface S3, the capacitorconductor 32 d being positioned closest to the circuit board 50, islarger than that in the mounting structure 1. As a result, H1/H2 issmaller in the mounting structure 1 a than in the mounting structure 1.Thus, the acoustic noise is more effectively reduced in the mountingstructure 1 a.

Second Modification of a Preferred Embodiment

A mounting structure 1 b according to a second modification of apreferred embodiment of the present invention will be described belowwith reference to the drawings. FIGS. 9A and 9B each illustrate anelectronic component 10 b mounted in the mounting structure 1 b.

In the mounting structure 1 a according to the first modification, thedistance between the bottom surface S2 and the capacitor conductor 32 dis larger than that between the top surface S1 and the capacitorconductor 30 a. Stated another way, an outer layer portion of thelaminate 11 on the lower side is thicker than an outer layer portionthereof on the upper side, and both the outer layer portions areasymmetrical. Therefore, when a mother laminate is fabricated in amanufacturing process for an electronic component 10 a according to thefirst modification, there is a risk that, if heat is applied to themother laminate, the mother laminate would be entirely warped andsubsequent processes could not be carried out.

To cope with such a problem, in the mounting structure 1 b according tothe second modification, an appropriate number of dummy conductors 31are disposed in the ceramic layers between the bottom surface S2 and thecapacitor conductor 32 d. As illustrated in FIG. 9A, the dummyconductors 31 may be each separated or disconnected in a central portionof the laminate 11 in the x-axis direction, and both ends of each dummyconductor 31 may be connected respectively to the outer electrodes 12 aand 12 b. Alternatively, as illustrated in FIG. 9B, the dummy conductors31 may be disposed in a central portion of the laminate 11 in the x-axisdirection such that the dummy conductors 31 are held in an electricallyisolated state without being connected to the outer electrodes 12 a and12 b. Moreover, the dummy conductors 31 may be connected to only one ofthe outer electrode 12 a and 12 b.

With the second modification, since the dummy conductors 31 are disposedin the outer layer portion on the lower side, which is comparativelythick and is made up of only the ceramic layers in the laminate 11, theouter layer portion on the lower side is hardened and the problem ofwarping of the laminate 11 can be overcome.

Third Modification of a Preferred Embodiment

A mounting structure 1 c according to a third modification of apreferred embodiment of the present invention will be described belowwith reference to the drawings. FIG. 10 is a plan view of the mountingstructure 1 c according to the third modification.

The mounting structure 1 c differs from the above-described mountingstructure 1 in the construction of the land electrode 54. In themounting structure 1 c, the land electrode 54 a is divided into landportions 70 a and 72 a. The land portions 70 a and 72 a preferably areeach substantially rectangular and are arranged in the order from thenegative side to the positive side in the y-axis direction. Further, theland portions 70 a and 72 a are overlapped with adjacent corners of thelaminate 11, respectively, when looking at the laminate 11 in a planview from the z-axis direction (i.e., from the direction normal to theboard body 50). In more detail, when looking at the laminate 11 in aplan view from the z-axis direction, the land portions 70 a and 72 a areoverlapped respectively with corners of the laminate 11, which arepositioned at both ends of the short side of the laminate 11 on thenegative side in the x-axis direction. The land portions 70 a and 72 aare connected to the outer electrode 12 a through solders 61 a and 62 a,respectively.

When looking at the laminate 11 in a plan view from the z-axisdirection, however, the land portions 70 a and 72 a are not overlappedwith a center of the end surface S3 (i.e., a point at which diagonallines of the end surface S3 intersect). Accordingly, the solders 61 aand 62 a are also not overlapped with the center of the end surface S3when looking at the laminate 11 in a plan view from the z-axisdirection.

Similarly, the land electrode 54 b is divided into land portions 70 band 72 b. The land portions 70 b and 72 b preferably are eachsubstantially rectangular and are arranged in the order from thenegative side to the positive side in the y-axis direction. Further, theland portions 70 b and 72 b are overlapped with adjacent corners of thelaminate 11, respectively, when looking at the laminate 11 in a planview from the z-axis direction (i.e., from the direction normal to theboard body 50). In more detail, when looking at the laminate 11 in aplan view from the z-axis direction, the land portions 70 b and 72 b areoverlapped respectively with corners of the laminate 11, which arepositioned at both ends of the short side of the laminate 11 on thepositive side in the x-axis direction. The land portions 70 b and 72 bare connected to the outer electrode 12 b through solders 61 b and 62 b,respectively.

When looking at the laminate 11 in a plan view from the z-axisdirection, however, the land portions 70 b and 72 b are not overlappedwith a center of the end surface S4 (i.e., a point at which diagonallines of the end surface S4 intersect). Accordingly, the solders 61 band 62 b are also not overlapped with the center of the end surface S4when looking at the laminate 11 in a plan view from the z-axisdirection.

The mounting structure 1 c can more effectively reduce the acousticnoise in comparison with the above-described mounting structure 1 asdiscussed below. In the mounting structure 1 c, each land electrode 54is divided into the land portions 70 and 72. Therefore, areas in whichthe outer electrodes 12 and the land electrodes 54 are connected to eachother through the solders 61 and 62 in the mounting structure 1 c aresmaller than areas in which the outer electrodes 12 and the landelectrodes 54 are connected to each other through the solders 60 in themounting structure 1. As a result, vibration generated in the electroniccomponent 10 is less transmittable to the circuit board 50 in themounting structure 1 c than in the mounting structure 1. Hence, theacoustic noise is reduced to a lower level in the mounting structure 1 cthan in the mounting structure 1.

In addition, when an AC voltage is applied to the electronic component10, the center of each of the end surfaces S3 and S4 (i.e., the point atwhich diagonal lines of each of the end surfaces S3 and S4 intersect)vibrates in a larger magnitude. Therefore, when the electronic component10 is fixed to the land electrodes 54 at positions just under thecenters of the end surfaces S3 and S4, the vibration is moretransmittable to the circuit board 50 from the electronic component 10.In view of such a point, each land electrode 54 is divided into the landportions 70 and 72 in the mounting structure 1 c for the electroniccomponent 10. When looking at the laminate 11 in a plan view from thez-axis direction, the land portions 70 and 72 are not overlapped withthe centers of the end surfaces S3 and S4, respectively. Thus, thesolders 61 and 62 are not overlapped with the centers of the endsurfaces S3 and S4, respectively, when looking at the laminate 11 in aplan view from the z-axis direction. As a result, transmission of thevibration from the electronic component 10 to the circuit board 50 issignificantly reduced and prevented.

For more positively confirming the advantageous effects of the mountingstructure 1 c, the inventors of this application conducted experimentsas follows. In more detail, the inventors prepared a first sample and asecond sample described below. An AC voltage of 1 Vpp was applied to theelectronic component 10 of each of the first sample and the secondsample, and a sound pressure was measured while a frequency was changed.

The first sample has the mounting structure 1 illustrated in FIG. 1. Thesecond sample has the mounting structure 1 c illustrated in FIG. 10.FIG. 11 is a graph representing the experimental results. In the graph,the vertical axis indicates a sound pressure level, and the horizontalaxis indicates a frequency.

As seen from FIG. 11, the sound pressure level of the second sample islower than that of the first sample. It can be thus understood that theacoustic noise is reduced with the division of the land electrode 54.

Second Preferred Embodiment

A mounting structure 2 according to a second preferred embodiment willbe described below with reference to the drawings. FIG. 12 is asectional structural view of the mounting structure 2 according to thesecond preferred embodiment. FIG. 13 is a plan view of the mountingstructure 2 illustrated in FIG. 12 when viewed from the positive side inthe z-axis direction.

The mounting structure 2 differs from the above-described mountingstructure 1 in the orientation of the electronic component 10. In themounting structure 2, the lateral surface S5 positioned on one side ofthe laminate 11 in the direction perpendicular or substantiallyperpendicular to the lamination direction serves as a mounting surface.In the second preferred embodiment, the lamination direction is definedas the y-axis direction. Further, when looking at the laminate 11 in aplan view from the y-axis direction, a direction in which the long sideof the laminate 11 extends is defined as the x-axis direction. Whenlooking at the laminate 11 in a plan view from the y-axis direction, adirection in which the short side of the laminate 11 extends is definedas the z-axis direction.

As illustrated in FIG. 13, in the mounting structure 2, the landelectrode 54 a is divided into land portions 70 a and 72 a. The landportions 70 a and 72 a preferably are each substantially rectangular andare arranged in the order from the negative side to the positive side inthe y-axis direction. Further, the land portions 70 a and 72 a areoverlapped with adjacent corners of the laminate 11, respectively, whenlooking at the laminate 11 in a plan view from the z-axis direction(i.e., from the direction normal to the board body 50). In more detail,when looking at the laminate 11 in a plan view from the z-axisdirection, the land portions 70 a and 72 a are overlapped respectivelywith corners of the laminate 11, which are positioned at both ends ofthe short side of the laminate 11 on the negative side in the x-axisdirection. The land portions 70 a and 72 a are connected to the outerelectrode 12 a through solders 61 a and 62 a, respectively.

When looking at the laminate 11 in a plan view from the z-axisdirection, however, the land portions 70 a and 72 a are not overlappedwith a center of the end surface S3 (i.e., a point at which diagonallines of the end surface S3 intersect). Accordingly, the solders 61 aand 62 a are also not overlapped with the center of the end surface S3when looking at the laminate 11 in a plan view from the z-axisdirection.

Similarly, the land electrode 54 b is divided into land portions 70 band 72 b. The land portions 70 b and 72 b are each substantiallyrectangular and are arranged in the order from the negative side to thepositive side in the y-axis direction. Further, the land portions 70 band 72 b are overlapped with adjacent corners of the laminate 11,respectively, when looking at the laminate 11 in a plan view from thez-axis direction (i.e., from the direction normal to the board body 50).In more detail, when looking at the laminate 11 in a plan view from thez-axis direction, the land portions 70 b and 72 b are overlappedrespectively with corners of the laminate 11, which are positioned atboth ends of the short side of the laminate 11 on the positive side inthe x-axis direction. The land portions 70 b and 72 b are connected tothe outer electrode 12 b through solders 61 b and 62 b, respectively.

When looking at the laminate 11 in a plan view from the z-axisdirection, however, the land portions 70 b and 72 b are not overlappedwith a center of the end surface S4 (i.e., a point at which diagonallines of the end surface S4 intersect). Accordingly, the solders 61 band 62 b are also not overlapped with the center of the end surface S4when looking at the laminate 11 in a plan view from the z-axisdirection.

With the mounting structure 2 according to the second preferredembodiment, as described below, the acoustic noise is significantlyreduced while a high degree of freedom in circuit design is obtained.FIG. 14 illustrates a state where the electronic component 10 vibratesin the mounting structure 2.

In the mounting structure 2, as illustrated in FIG. 14, when an ACvoltage is applied to the electronic component 10, the center of each ofthe end surfaces S3 and S4 (i.e., the point at which diagonal lines ofeach of the end surfaces S3 and S4 intersect) vibrates in a largermagnitude. Therefore, when the electronic component 10 is fixed to theland electrodes 54 at positions just under the centers of the endsurfaces S3 and S4 (on the negative side in the z-axis direction), thevibration is more transmittable to the circuit board 50 from theelectronic component 10. In view of such a point, each land electrode 54is divided into the land portions 70 and 72 in the mounting structure 2.When looking at the laminate 11 in a plan view from the z-axisdirection, the land portions 70 and 72 are not overlapped respectivelywith the centers of the end surfaces S3 and S4, which are vibrationsources. Accordingly, the solders 61 and 62 are also not overlapped withthe centers of the end surfaces S3 and S4 when looking at the laminate11 in a plan view from the z-axis direction. Thus, in the mountingstructure 2, the solders 61 and 62 each acting as a transmission pathfor the vibration are positioned apart from the centers of the endsurfaces S3 and S4, which are the vibration sources. With such anarrangement, the vibration generated in the electronic component 10 isless transmittable to the circuit board 50. As a result, the acousticnoise is reduced in the mounting structure 2.

For more positively confirming the advantageous effect of the mountingstructure 2, the inventors of this application conducted experiments asfollows. In more detail, the inventors prepared a third sample and afourth sample described below. An AC voltage of 1 Vpp was applied to theelectronic component 10 of each of the third sample and the fourthsample, and a sound pressure was measured while a frequency was changed.

The third sample has the mounting structure 2 illustrated in FIGS. 12 to14. The fourth sample has a mounting structure obtained by modifying themounting structure 2, illustrated in FIGS. 12 to 14, such that theelectronic component 10 is mounted in the orientation illustrated inFIG. 12 on the circuit board 50, but the land electrodes 54 of thecircuit board 50 are each not divided. FIG. 15 is a graph representingthe experimental results. In the graph, the vertical axis indicates asound pressure level, and the horizontal axis indicates a frequency.

As seen from FIG. 15, the sound pressure level of the third sample islower than that of the fourth sample. It can be thus understood that theacoustic noise is reduced in the mounting structure 2 with the divisionof the land electrode 54.

Other Preferred Embodiments

It is to be noted that the mounting structure according to the presentinvention is not limited to the above-described preferred embodimentsand it can be variously modified within the scope of the presentinvention.

In particular, although the land electrodes 54 a and 54 b preferably areeach divided into two portions in the second preferred embodiment (seeFIGS. 12 to 15), only one of the land electrodes 54 a and 54 b may bedivided into two portions.

As described above, preferred embodiments of the present invention areuseful for the mounting structure of the electronic component and areespecially superior in an ability of reducing the acoustic noise whileensuring a high degree of freedom in circuit design.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A mounting structure including an electronic component mounted on aboard, wherein the electronic component comprises: a laminate includinga plurality of laminated dielectric layers, a mounting surface thatfaces the board and that is positioned on one side of the laminate in alamination direction, and a first end surface and a second end surfacethat are opposed to each other; a plurality of capacitor conductorslaminated together with the dielectric layers to define a capacitor, andled out to the first end surface or the second end surface; a firstouter electrode disposed to extend over the first end surface and partlyover the mounting surface, and connected to the capacitor conductors; asecond outer electrode disposed to extend over the second end surfaceand partly over the mounting surface, and connected to the capacitorconductors; wherein the board includes: a board body; and a first landelectrode and a second land electrode disposed on the board body, thefirst land electrode and the second land electrode being connectedrespectively to the first outer electrode and the second outer electrodethrough conductive materials; wherein a distance from the first landelectrode or the second land electrode to a top of the conductivematerial is not larger than about 1.27 times a shortest one amongdistances from the first land electrode or the second land electrode toexposed portions of the capacitor conductors, which portions are exposedat the first end surface or the second end surface.
 2. The mountingstructure according to claim 1, wherein the shortest one among distancesfrom the first land electrode or the second land electrode to exposedportions of the capacitor conductors, which portions are exposed at thefirst end surface or the second end surface, is a distance from thefirst land electrode or the second land electrode to an exposed portionof one of the capacitor conductors exposed at the first end surface orthe second end surface, the one of the capacitor conductors beingpositioned closest to the board.
 3. The mounting structure according toclaim 1, wherein the first land electrode is divided into a first landportion and a second land portion, and the first land portion and thesecond land portion are overlapped with adjacent corners of the laminatewhen looking at the laminate in a plan view from a direction normal tothe board body.
 4. The mounting structure according to claim 1, whereinthe conductive material is a solder.
 5. The mounting structure accordingto claim 1, wherein a distance between the mounting surface and thecapacitor conductor closest to the mounting surface is longer than adistance between a surface of the laminate opposed to the mountingsurface and the capacitor conductor closest to the opposed surface. 6.The mounting structure according to claim 5, wherein a dummy conductoris disposed between the mounting surface and the capacitor conductorclosest to the mounting surface.
 7. The mounting structure according toclaim 1, wherein the laminate has a substantially rectangularparallelepiped shape.
 8. A mounting structure including an electroniccomponent mounted on a board, wherein the electronic componentcomprises: a including a plurality of laminated dielectric layers, amounting surface that faces the board and that is positioned on one sideof the laminate in a direction perpendicular to a lamination direction,and a first end surface and a second end surface that are opposed toeach other; a plurality of capacitor conductors laminated together withthe dielectric layers to define a capacitor, and led out to the firstend surface or the second end surface; a first outer electrode disposedto extend over the first end surface and partly over the mountingsurface, and connected to the capacitor conductors; a second outerelectrode disposed to extend over the second end surface and partly overthe mounting surface, and connected to the capacitor conductors; whereinthe board includes: a board body; and a first land electrode and asecond land electrode disposed on the board body, the first landelectrode and the second land electrode being connected respectively tothe first outer electrode and the second outer electrode throughconductive materials; wherein the first land electrode is divided into afirst land portion and a second land portion; the first land portion andthe second land portion are not overlapped with a central portion of thefirst end surface when looking at the laminate in a plan view from adirection normal to the board body; and the conductive material is notoverlapped with a central portion of the first end surface when lookingat the laminate in a plan view from the direction normal to the boardbody.
 9. The mounting structure according to claim 8, wherein theshortest one among distances from the first land electrode or the secondland electrode to exposed portions of the capacitor conductors, whichportions are exposed at the first end surface or the second end surface,is a distance from the first land electrode or the second land electrodeto an exposed portion of one of the capacitor conductors exposed at thefirst end surface or the second end surface, the one of the capacitorconductors being positioned closest to the board.
 10. The mountingstructure according to claim 8, wherein the first land electrode isdivided into a first land portion and a second land portion, and thefirst land portion and the second land portion are overlapped withadjacent corners of the laminate when looking at the laminate in a planview from a direction normal to the board body.
 11. The mountingstructure according to claim 8, wherein the conductive material is asolder.
 12. The mounting structure according to claim 8, wherein adistance between the mounting surface and the capacitor conductorclosest to the mounting surface is longer than a distance between asurface of the laminate opposed to the mounting surface and thecapacitor conductor closest to the opposed surface.
 13. The mountingstructure according to claim 12, wherein a dummy conductor is disposedbetween the mounting surface and the capacitor conductor closest to themounting surface.
 14. The mounting structure according to claim 8,wherein the laminate has a substantially rectangular parallelepipedshape.